I guess men have had to do things like lead armies and governments first and foremost beacause of their strenght, and secondly beacause of pre-existing customs. ei culture.

^ and that's the reason why men have had to save face up until now and Fighting/work/sports/leading goes to men while nurturing and open sexuality goes to women.

I'm confused by exactly what you mean by male supremacy. Do you mean men being succesful in sports moreso than women? (or rather, mens sports being more popular).

Men, to put it simply are just better athletes, look at every single olympic record. The ones for men are better than the ones for women. (who knows, there might be an exception or two). That's the reason that men and women don't compete against each other at a professional level. The same way in combat sports, there are weight classes.

And save face? :S Save face for what exactly?

Yes, childbirth is painful, but going through something painful doesn't mean you're a better athlete, or even that you're better at taking pain. If someone shot me, if wouldn't make me better at getting punched.

In fact, men actually have a higher pain tolerance than women (someone posted a thread about this a few days ago, if you wanna go check it out).

Also, what do you mean by open sexuality? Of men and women that I know, women are usually far more closed off about their sexuality than men are.